This invention relates to a method apparatus for formatting a stereoscopic video frame and for stereoscopic viewing of the formatted video frame.
Present day methods of formatting and stereoscopically viewing video images evolved from early devices which combined photographs or images of the same object or scene taken from slightly different points of view (corresponding to the positions of the two eyes) by means of mirrors placed at a suitable angle or by two tubes, each containing a lens, through which the two photographs or images were viewed by the corresponding eyes to obtain a single image to give the impression of solidity or relief as in ordinary vision of the scene or object itself.
The most commonly employed methods of formatting a stereoscopic video frame involve generating the left and right images of a stereo video image pair using a pair of spaced apart video cameras directed towards the left and right sides of a common subject and displaying the left and right images separately on a single video screen, either in over-under or side-by-side relationship. Polarizing filters are used to polarize the light emitted by the two images at 90 degrees with respect to each other, and the images are viewed through viewing devices such as those disclosed in U.S. Pat. No. 4,740,836 to Craig; U.S. Pat. No. 4,559,556 to Wilkins; U.S. Pat. No. 4,523,226 to Lipton et al.; U.S. Pat. No. 4,583,117 to Lipton et al.; and U.S. Pat. No. 4,709,263 to Brumage; which have correspondingly polarized lenses so that the left image is viewed by the left eye through the left lens and the right image is viewed by the right eye through the right lens.
Such viewing devices require complicated adjustments to focus and combine the left and right images which are difficult to make and, once made, require the viewer to remain at a fixed distance from the video screen While it is possible to pre-adjust the viewing device and make the pre-adjustment fixed, when such pre-adjustment is fixed, the distance from which the video screen must be viewed is dictated by the pre-adjustment and the size of the video screen. In either case, it has been found that the distance from which the video screen must be viewed with such viewing devices is uncomfortably close.
Further, such viewing devices are bulky and uncomfortably heavy, and since prisms are used, it is impossible for the viewer to look away from the video screen and observe anything else in the viewing area without visual distortion.
A further deficiency resulting from the over-under format, as disclosed in U.S. Pat. No. 4,559,556 and U.S. Pat. No. 4,740,836 is the loss in the vertical dimension in the stereoscopic video image which is perceived by the viewer through such viewing devices For example, in the over-under format using a conventional cathode ray tube having a horizontal to vertical dimension ratio of approximately 1.85 to 1, the left and right images are presented on the upper and lower halves of the cathode ray tube having horizontal to vertical dimension ratios of approximately 3.7 to 1 each, while in the side-by-side format using the same conventional cathode ray tube, the left and right images are presented on the left and right halves of the cathode ray tube having horizontal to vertical dimension ratios of approximately 0.93 to 1 each.
Finally, it is obvious that such viewing devices cannot be used by a viewer who is required to wear glasses.
In order to overcome some of the foregoing deficiencies, viewing systems have been devised which can be characterized as "table-top" such as those disclosed in U.S. Pat. No. 4,568,970 to Rockstead and U.S. Pat. No. 4,743,964 to Allard et al. which use an array of mirrors to create optical paths for the left and right images of the stereovideo image pair and provide left and right fixed openings through which the viewer simultaneously views the left and right images. Such devices replace the unwieldy head-worn viewing devices with table-top viewing devices, but the viewer must remain a fixed distance from the viewing device in order to properly view the stereoscopic image pair.
Still other devices have been proposed such as those disclosed in U.S. Pat. No. 2,845,618 to Huffman; U.S. Pat. No. 4,190,856 to Ricks; and U.S. Pat. No. 4,658,291 to Morishita which use a beam splitter to combine the left and right images on a single viewing surface.
A major flaw found in all of the prior art devices results in distortion which is found when the left and right images are combined to form a single stereoscopic image. This distortion results from the fact that the face of the cathode ray tube which is used as the display screen is curved and not flat and the corners are rounded and not square. Accordingly, the left and right video images are geometrically distorted to some extent in the corners and along the outer edges of the video display screen. Because of the geometric distortion created by the curved screen, the left and right images displayed on the upper and lower or left and right halves of a single video screen cannot be optically combined in overlapping fashion without noticeable distortion.